Method of drying and impregnating wood



D. MCDONALD METHOD OF DRYING AND IMPREGNATING WOOD Filed June 4, 1954 Y Nov. 11,1958

6 Sheets-Sheet 1l n000000 ooaoeoo mwmtohm. i .zuem,

D. MCDONALD METHOD OF DRYING AND IMPREGNATING WOOD Nov. 1l, 1,958

6 shets-sheet- 2 Filed June 4, 1954 Nov. 1l., 1958 n.--MCpoNALD 2,860,070

METHOD oF DRYING AND IMPREGNATING woon Filed June 4, 1954 e sheets-sheets Nov. 11, 1958 D. MCDONALD 2,860,070

METHOD oF DRYING AND IMPREGNATING woon Filed June 4, 1954 e sheets-sheet 4 Nov. 11, 1958 D. MGDONALD 2,850,070

METHOD o'F DRYING AND IMPREGNATING woon Filed June 4. 1954 @sheets-sheet 5 Nov. 11, 1958 D. MGDONALD 2,860,070-

METHOD oF DRYING AND IMPREGNATING woon Filed June 4. 1954 6 sheets-sheet 6 United States. Patent O,

2,860,070,A e METHoD oF DRYING ANDnrPREGNATING Woon Dan McDonald, Aurora,.l1l., assignor, by mesne assignments, to Barber-Greene Company, Aurora, Ill., a corporationv of Illinois v 4 Claims. (Cl. 117-59) INDEX l Subject '..Column Introduction 1-3 The apparatus 3 Drying 5 Soaking y7 Drying after soaking 8 Treating v 8 The automatic control l1 Drying ll Soaking 13 Drying resumed 13 Draining of retort y 14 Treating 14 Treating solvent soak 14 Vapor flow meter and switches 17 Retort solvent level control A18 This invention relates to the treatment of wood with the aid of solvents for removal of moisture, resins" and other extractives therefrom, and .for otherwise treating the wood. f

As heretofore commercially practiced,"the` most commonly used methods of drying Wood have been air drying, that is, ordinary seasoning in air andkiln drying.

In addition'to drying, other known treatments for wood have included impregnation with materials adaptedl to protect the Wood against decay and attack by insects.-

Application June 4,19s4,seria1N0.434,390 e 10 The above mentioned conventionalv drying methods,

even when carefully operated, are recognized generally in the industry as being far from satisfactory because such methods either induce or do not protect the wood from the harmful elects of checking, warping, cupping and mold growth both during and after drying.. Another serious and costly disadvantage is the large amount of time such conventional drying processes require. Other defects, well known to the industry, need not be recited here but may be alluded to later during the ensuingdescription of this invention. However, all 'such defects have caused serious losses to the lumber industry` and have involved for decades .constant searching lfor better drying and wood preserving methods.

A considerable proportion of the wood handled by the lumber industry contains resins, gums and terpenes', Which not only are not removed by the` prior conventional drying processes, but are often oxidized and changed in composition.

During the aforementioned constant searchk by the industry for better methods, the possibility of using solvents orother liquids and vapors for various treatments of wood has been considered by prior inventors. Nevertheless, according to availablel information, their efforts have met with no success or have resulted at best in only limited and partial benefit to the wood, where beneficial at all.,v Evidence of such piror efforts can be found among such U. S. Letters Patent and pubice 2 Besemfelder, 1,059,820, issued April 22,1913.; Hollerer, 2,137,404, issued November 22, 1938; Helson 2,216,775, issued October 8, 1940; Anderson, 2,500,783, issued March 14, 1950; Barksdale, 2,507,190,l issued May 9, 1950; and Report R1665 of U. S. Forest Products Laboratory at Madison, Wisconsin, dated February 1947.

My invention, as will presently appear, involves principles and techniques in the use of solvents wholly novel, and markedly different from the teachings of said patents and publications, and productive of numerous advantages and results incapable of attainment by the procedures taught in said patents and publications;

My invention involves the use of non-ilammablewater immiscible solvents in liquid form in drying processes which may be applied to fresh cut green wood, sawed or unsawed, and to wood not freshly cut butY in rneed of drying, and for other treatmentsjfor improving the wood and conditioning it for various ultimate uses.

In accordance with my invention, the wood to be treatedis immersed in a'liquid solvent bath, and while 'thevbath is' maintained at an elevated temperature, mois- Y ture isY removed from the wood and, if the Wood be resinous or contains other solvent soluble extractives the resins and otherextractives may also be extracted. While moisture and other extractives are being removed, the wood is being improved and conditioned by the solvent in a novel manner invarious important respects and is especially conditioned for otherV s ubsequent'treatments including impregnation and coating by preservatives and other additives of various types. Y i' vWood dried in accordance with this invention, even if not further treated, is different from and superior to wood dried by any other commercial methods yknown heretofore, as has been convincingly demonstrated by various tests. For example, theV harmful eiects of checking, splitting, cupping, twisting, case hardening, vexplosion or collapsing of the cellular structure, and harmful stresses of various kinds inherent in the wood originally and which to some extentinvariably or at least frequentlydevelop from other drying methods, are either eliminated or greatly diminished in the invention. Y

Wood dried in .accordance with this invention vand subjected simultaneously to solvent extraction, Ais ybetter conditioned to absorb uniformly various impregnating and coating materials, as will more readily appearY hereinvention is that dimensional stability of the wood, long recognized in the industry as a desideratum, is achieved to an unusually high degree both during and' subsequent to the drying operation.

The generalobject of the invention is to provide im? proved processes for drying, conditioning, and treating 1 wood. i V l Av particular object is to provide a new Vprocess and procedure for drying Wood while immersed in a'liquid solvent bath.

Another object is to provide a new process in which moisture removal and resin removal from the wood may be accomplished in the same apparatus concurrently or in steps. v Y

Another important object -is to provide methods and apparatus for controlling the process steps and operations automatically. e Y

Another object is to provide a process in which a liquid solvent bath is employed for drying wood and the same solvent is used asa carrier for impregnating material. Y

Another object of the invention lis to provide anew process and apparatus in which resin extraction may be practice of this coordinated in various ways with moisture removal `and with impregnation.

Another object is to provide a process for dryingV wood more rapidly than has been customary heretofore and under .controlled 'conditions which prevent damage o to the wood." v Y Y .I

Another object is to utilize a liquid solvent bath -in drying of wood whereby the vaporigation ofy moisture asp-an arzeotrope vapor from the wood may -be effected at la' selected temperature, dependent uponfth'e pressure andthe solvent'employed, which .will be substantially below the boiling point `ofuwater at such selected pres-N Other Obiecf Gfffhe invenfien not yet mentianed'may. be alluded to hereinafter as may b e observed and ap-M.

Ol'Of As111011. aPPaUlS 1.10r t0 the precise methods..de..

scribed.

, Figure lis aschematic flow diagram in which the, ap

prevent the boards from floating out of theA stacked load. The stickers preferably are 'suspended from the bars 19l paratus indicated is shown not according to a uniform dimensional scale nor necessarily in preferred relative positions, but rather in such a compact arrangement as 16.11.@ ,flf toa .snslesure Qw. diagram.

Figure 2 is a cross section/al view on an enlarged scale '3-0 Figure 3 is a schematic drawing of part of the elecf trical control` circuit forming a portion ofthe. invention.

of the retort shown` in Fig. 1,.

Figure 4 'is alschem'atic drawing of the remainder of the electrical control circuit. v

Figurev Sis a schematic illustration ofv a liquid level control system forming a part of the invention.

Figure "16h is adiagrammatic illustration of an orificev deviceand owvmeteremployed in the invention.

Figure 7 is ay diagrammatic illustration of. a switch mechanismjassociated,withthe flow meter.

switch mechanism in another' position;

Figure 9 is a schematic illustrationV of an alternative apparatus, which may besubstituted for the apparatus of Figs. 6,*7 and 8 Figure 8v is a diagrammatic illustration ofthe sarnerV The equipment shown in the ow diagram of Fig. ll

is adapted for usein dryingof woods which are difcult to dryl or easy to dry, for drying woods having high, low

or no resin content, and for ir'npregnating any of these woods with additives, such as those which retard or prevent moisture re-absorption, those which prevent m'o-ld,YAY

those which protect the wood against attack by termites and insects, yand otheradditives which may improve the hardness, strength, iinish or general appearance of the wood or impart to it any other useful-characteristics.

However, to bring into the descriptionof ya single processthe use of all the equipment shown, `I' shall rst describe the drying of typicalzsouthern yellow pine, having a high resin content, and its subsequent impregnation with linseed oil, to retard subsequent re-absorption of moisture. p i

The apparatus The retort, generally indicated as 11, is a tank of any` desired dimensions and shape7 formed of steel or other suitable materials having closed sides, top and bottom and -preferablyencased in a suitable `layer of'insulation/1V2. In view ofthe pressure to which it may be subjected, both'above and below atmospheric, vit should be suitably constructed and braced. A pair .of rails '13 extending longitudinally .within the' retort constitute a,

track for the wheels 14 of lumber bearing cars.` This track will be aligned with conventional track rails outside the retort, as is customary in connection with lumber Akilns Vand a tightly scalable door, not shown,` may 'be provided at either or both ends of the retort for admitting and discharging the loaded cars and sealing the retort before it is iilled with solvent. When the car or cars are at rest in the retort their wheels will be underneath hold-down flanges 15 secured to the retort walls, which prevent the lumber-laden car from floating upwardly when immersed in the solvent.

The details of construction of the cars are subjectV Y to Wide variation, but in general should include a oor 16 which should have numerous perforations or passages to permit free ow therethrough of solvent, and side walls v17 which should likewise be perforated or which may be largely open frames. The lumber should be stacked in such a manner as to facilitate its uniform treatment by the solvent. One'appropriate method is indicated, wherein boards 18, for example, preferably of uniform thickness and of the same species, are shown stacked longitudinally on edgeand are uniformly spaced by vertically extending Spacers or stickers, not shown, to allow the heated solvent as it rises to contact opposite vertical faces of each of the boards as uniformly as is practicable. Suitable means such as bars 19 detachably secured to the Vcar side walls and extending across the Vtop Vof the stacked lumber may be Vused to to hang vertically therefrom, and preferably are rust proof metal tubesof cylindrical' shape so that they will have merely line contact with the boards'.

Preferably, bundles of heating coils 21 utilizing steam, for example, as a heating medium, will be placed between the angular baffles 22, which are suitably iixed in the retort for heating the solventand causing it to 'rise in convection currents through thel stacked lumber the wood and rising withthefsolvent aid the circulationH of Vthe solvent.

The position,ofthe, liquid level control mechanism shown diagrammatically in Fig. 5 is'indicated in Fig. 2

in partwbya casing 24, which communicates with the interior of the retort V11 below Vand above `the liquid level therein by pipes 25 and contains a hollow float-element 26. This oatfandassociated mechanism-,.-.shownlin Fig. 5

and hereinafter described inV detail, cooperate with other liquid supply valves, as explainedflater, but especiallyv control-a by-pass throttling valve 27 (Figs. l `and v5) to maintain a liquid level in the .retort suiicient to com pletely submergethewood and overiiowthe tops of baies are employed to supply solvent tothe retort. Other suitable liquidlevel controlmeans may. be employed, if

2li. Valve 27 is smaller than. the.: other. valves which desired. Y

In a woodtreating plant of commercial size, the-valve 27 and various other valves described asautomatically operated should, because of their large sizes, be operated by some appropriate source ofpowen compressed air, forvexample,'in which case the auxiliary Valving for supi plying and regulating the air tofactuate `such large valves may be electrically controlled, as by solenoids, for 'ex-5' ample, responsive to thermostatic'all'yfcontrolled or lpressure controlled or time controlled relaysorjother appropriate mechanisms; i

-The automatic operation of these valves and other controlsin4v proper sequences will-be described hereinafter in connection with'the electrical circuits of Figs. 3 and 4 and the schematic diagram1 in Fig. 5. For conciseness and clarity, thefunctioris `of the valves and other apparatus will nowfbe described without explaining here the chlorinated hydrocarbon, perchlorethylene, having aA boiling point Vofabout 250 F. and a water-solvent azeotrope point Vof about 190' F. at atmospheric pressure. Hand valves'28 and 29 in pipe 31 will be open, power operated valves 32 and 33 'will be closed, power operated valve 34 in vapor line 35 will be opened andas solvent flows into the retort the air will be displaced therefrom through line 35, through a condenser (later described as 41) in part-into a system of pressure equalizer lines consisting of interconnected pipes 36. Some of the air will ow into the raw solventtank 39 from which solvent is flowing. All of the displaced air initially ows into condenser 41, which may be a' conventional water cooled surfacel condenser, and some ofit flows thereafter through the gravity separator. 42 (later described), vapor line 43,

through one'or both check valves 44 and 45,l one or both carbon, absorbers 46 and 47, one or both check valves48V and 49, line 51 and exhaust blower 52 to atmosphere. Solvent for `the operation Ais originally supplied to tank 39 from storage tank 53l by means of pump 54 and line 55. To supply the retort from the tank 39 the solvent may be allowed to ilow by gravity through pipe 56 through the normally open hand valve 57, the now open power operated valve 58, pipe 59, entering pipe 31 above strainer 62, thence into the retort. When the retort is filled to or nearly to thedesired level, the large ow capacity valve 58 will be closed ordinarily by a timer mechanism or by the liquid level control system shown in `Fig. 5. The liquid level controlled throttling valve 27 having a much smaller ow capacity is called upon after the timer mechanism, later described, has closed valve 58. The throttling valve supplies solvent to establish, and or maintain the liquid level high enough to overflow batlles 23 and keep the lumber entirely submerged and to add liquid solvent to the retort as solvent is absorbed into the wood and is also evacuated from' the retort in vaporous form. Meanwhile, or shortly thereafter, power operated steam valve 63 is opened to supply steam to the heating coils 21 in the bottom of the retort, and power operated condensate valve 64 is likewiseopened, allowing steam condensate to escape through a conventional or suitable condensate trap 65.

Too rapid application of heat to the fresh load of lumber should be avoided, hence thathazard is minimized if the solvent as it enters the retort and contacts the lumber be at a temperature well below its azeotrope boiling point. It is desirable that the entire 'load be heated gradually and uniformly and the rate of evaporation of moisture from the wood be moderate enough to avoid harmful checking of the surfaces, as would occurk if drying were too rapid.

Suitable thermostatic control equipment symbolized by the thermostatic element 66 and steam valve 67 which it controls, may be relied upon to control -the steam supply to bring the body of the solvent eventually up to a desired temperature range between the azeotrope boiling point and the solvent boiling point, at theV existing pressure.

As this drying step begins, azeotrope vapor forms both at the outer surface of the wood and interiorly wherever the penetrating solvent contacts water or water vapor, and where sufficient latent heat is supplied at such points to cause the azeotrope vapor to evolve. The evolved azeotrope vapor rises into the vapor space within the retort above the level of the solvent and is evacuated through pipe 35 connected to the vapor trough 35 which extends longitudinally and .centrally of ltlieretr'r't.V 'AnyV condensate forming in the .trough may bereturrnedA to the liquid body in the retort by appropriate drainmeans, not shown. Pipe 35 delivers the vapor into condenser 41, where substantially all of the azeotrope vapor is cond ensed. Thetcondensate ows through `pipe 68 into gravity separator 42, wherein the heavier perchlorethylene separates from the Water and is withdrawn by pipe Y69, and pump 71, and delivered by` pipe 72 to solvent As shown in Fig. l, the lower open end of pipe 68 is curved to avoid delivering the condensate vertically downwardly, and terminates at or above the interface level 68a between the separated solvent and water. Above the maximum water level, jdetermined by the overflow pipe 74, the pipe 68 has aixed thereon and sealed thereto a trough 68b, open at the ftop.- Just above the floor of the trough is a seriesy of holes such as 68d and above them another series of holes68c. ',Vapors accompanying the condensate will escape through the upper holes, while any condensate escaping therewith will immediately drain back into pipe 68 through holes 68d. v

As some of the solvent may notl be condensed in 41, and air and other gases 4expelled from the wood may accompany solvent vapor into separator 42, the carbon absorber system associatedtherewithand Vwith the exhaust fan 52 will evacuate these gases and vapors from the separator 42, absorb the solvent vapor and dischargev the air and other non-condensibles to the atmosphere without wasting any appreciable amount` vof solvent. Hence the solvent cost of the process is one of initial investment and not a continuing or recurringnew expense of any substantial amount.

The combined effect of the condenser 41, absorber 46 or 47,`and the exhaust blower 52 is to lower the pressure in the retort 11 slightly below atmospheric pressure. This reduced pressureserves to prevent leakage of solvent vapors to the atmosphere should leaks inadvertently develop in the solvent vapor lines. If it be desired to lower the retortvinternal pressure even more and thus reduce the azeotrope boiling point, suitable expedients may be employed therefor such, for example, as inserting a suitable vacuum pump between the condenser 41 and the separator 42. This expedient will be described later. v

As the operating example now being described involves typical southern yellow pine having a substantial resin content, while the drying operation is proceeding, some resin is also being dissolvedl into the solvent, which, at the elevated temperatures existing, has a high solvent capacity for the natural wood resins, terpenes, gums,

pitch and other similar extractibles which, for the sake of brevity, are herein referred to merely as resins.

To satisfy many commercial requirements it will be desirable to solvent extract the bulk of the resins from the wood while the wood is being dried. For other requirements it may be satisfactory merely tov re-distribute the resins from localized concentrations of the same to a more uniform dispersion throughout the wood. Resin The greater part, termed free water, exists between orV outside of the cells, while a lesser part designated as Soaking While itis-possible to dry non-resinous and resinous woods down to a final Vspecified moisture content of 7-12% moisture ina single continuous drying step, without soaking, in general the drying will be improved and shortened and the resin extraction and/or, dispersion made more thorough in the case of resinous woods, if the drying procedure be interrupted by one or more soaking periods. When soaking is employed the soaking may be conducted at various intervals in Vthedrying cycle, but

most advantageously after the moisture content has been reduced to 50% or less.

In operating in accordance with my invention, the rate of moisture evaporation from the wood at a given period in the process is an ascertainable factor on which certainV controls of the process may be and desirably are based. During the early evaporation of moisture, largely` free moisture, which is evacuated in theazeotrope vapor, the evolution of this vapor, consisting of 5.3 parts of perchlorethylene to 1 part of water,'is very rapid, and continues at a high rate until the free moisture has been largely removed.v However, as the critical moisture content is approached, the volume of azeotrope vapor evolved per unit of time drops off sharply.V This stage in the process constitutes a very favorable time to initiate the first soakingv period, although I sometimes nd it advantageous to anticipate this period, that 1s, before the rte-` maining moisture content has reached the critical mo1s' ture content. Y

At whatever be the selected instant the rate of vapor flow is'in a measurable proportion to the instant moisture content and by means of the-vapor flow measuring apparatus hereinafter described in detail I may select that instant and interrupt the drying process by stopping the evolution of azeotrope vapor, and cause solvent to penetrate the wood to facilitate further drying'and, in the `case of a resinous wood, facilitate the solvent extraction of the resins. A

Thus, when the initial drying period has continued long enough to lower the moisture content of the wood to a desired range which may, if desired, be at some point between 25 and 50% or higher, the rate of flow of azeotrope vapor through the -oriice plate device in line 35, generally indicated as '77, will be Vutilized to effect the actuation of the apparatus shown :in Figs. 6 and 7 and,

initiate any one or more of several procedures, as may be desired, to condense vapors then within the wood and allow the solvent to'penetrate the wood more readily and deeply. This penetration step is herein termed soak lng.

In one procedure the solvent bath may be cooled to at least several degrees below the azeotrope boiling point 190 F., which will cool'the wood and cause the desired condensation of vapors therein, inducing a lower pressure in the wood. To do this, steam supply valve 63 and condensate outlet valve'64 will be closed, and poweroperated water supply valve 78 and power-operated water outlet valve 79 may be opened, enabling cold water to flow through the cooling coilsV 79', thus cooling the solvent bath to below 190 F. When it is deemed that the solvent has sufficiently penetrated the wood the foregoingV mentioned valves will be re-operated to cut olf the cold water and restore the-steam supply, raising the solvent bath temperature high enough to cause the evolution of azeotrope vapor to resume.

parent that the above two cooling methods may be com-1 bined if desired.

-Al further alternative procedure for condensing vapors Vin the wood is to raise the pressure in the retort high enough to effect the desired vapor condensation. Thisy has an advantage over the cooling method in that vapor condensation may be accomplished faster merely byclosing valve 34 and injecting steam at 15 to 25 pounds pressure, for example, into the retort, hence only a few minutes is required.

A still further alternative procedure, which will be referred to later in connection with, andl which is provided for in, the circuit diagrams, involves closing thev vapor outlet valve 34when itis Vdesired to soak, cutting off the supply of steam to coils 21, if desired, and allow-v,

ing the azeotrope vapor retained and accumulating in the retort to become superheated by the residual heat in The action of 'the absorberf and condenser normally maintains a slight suction on the the solvent and the retort.

retort, but with the vapor valve 34 closed a pressure builds up in the retort suicient to compress the vapors in the wood and cause the solvent -to penetrate the wood. If

desired the equipment may be arranged to leave the steam v supply on during the soaking period.

Drying after soaking After soaking the wood a desired length of time, which may, for example, be about one-halfhour or somewhat less for soaking pinelumber one inch in thickness, and

proportionately longer for thickerlumber, the vaporv valve 34 may bere-opened. and the heating steamturned on again, whereupon .the lumber resumes evolving Vazeotrope vapor-and continues to do so until the moisture content is further reduced to a desired extent, which in many instances may be as low as 7 to 10% moisture if the wood is not to be impregnated.

When the moisture content is reduced to the desired level, the solvent will be drained from the retort throughv normally open valves 28 29, strainer 62 and poweroperated valve 32 to r`droptank 80, while valver33 is kept closed. This solvent will contain most of the gums, resins and terpenes originally contained in the'wood.

If the wood is to be impregnated with an additive, the foregoing moisture evaporation should be terminated preferably at about l5 to 25% residual moisture content.

Treating The next step is treat the lumber in another bath of k solvent, preferably more of the same solvent,`but containing an appropriate impregnating material. One such material is boiled linseed oil, which is soluble in the halogenated hydrocarbons. When ,the yellow pine be'- comes impregnated with such oil to they extent of about eight pounds of oil per thousand board feet, and is later exposed to moisture, re-absorption of moisture is greatly reduced or largely eliminated, the lumber mill will remain f dimensionally stable and is improved forV machining and More or less oil and' other wood working techniques. other oils may be used. Also, insect and termite repelling chemicals, fungicides, mold preventatives, various water repellants, dyes and other chemicals, including plastics, also soluble in the solvent, may be substituted for the linseed oil or used in addition thereto and simultaneously. VAll of these additives are intended to be-referred to herein by the term wood preservatives and preferably should have boiling points higher than the azeotrope boiling points Vand preferably higher than the solvent boiling point, and should not form ternary azeotropes with the solvent and water.

One or more additive storage tanks such as v8]. may

be provided andthe liquid material contained therein may be metered through a conventional liquid ow meterv 82 while being delivered by pump 83 into the treating solution tank 84 where it becomes dissolved in abody` of the solvent contained therein and delivered thereto by any appropriate means, forexample, from the drop tank 85 by pump 85a and line 85b. If the tank 84 contains-fI pure solvent a desired relative proportion of additive will# be metered and pumped into it. If the solution in 4tank 84 has previously been used for treating lumber and its former additive ingredients thereby'diminished theyvmay be replaced from the tank 81. The additives must be soluble in the solvent, have higher boiling points than the t solvent and not be of a character to form ternary azeotropes with the water and solvent.A r

To treat the lumber with a solvent solution containing one or more of additives of the character above described, the treating solution is conductedV from tank 84 through pipe 86, power-operated valve 87, pipes 59 and.' 20 31 into retort 11, iilling the retort high enough to sub-v merge the load of Wood. Preferably during the foregoing described draining and relling ofl the retort the steam supply to the heating coils 21 will be cut oit, but will be turned on again when the retort is relilled. i

Hence, with the retort lled with the treating solution and steam in the coils the wood is re-heated in this bath by the solution, which may be heated to a temperature range of about 210 to 245 F. During the relatively short heating period which follows, some of theremaining moisture in the wood begins to emerge therefrom as part of the azeotrope vapor, hence the vapor valve 34 is held open to allow such vapor to flow to the condenserA and carbon adsorber system. As solvent thus escapes from the retort in the azeotrope vapor the throttling valve 27 should be open during this period to supply make-up sol- 34 will be re-opened and further evaporation of moistureV will occur, accompanied by evaporation of solvent from the interior of the wood as the azeotrope vapor is being evolved. This evaporation period is continued until nearly the nal specified moisture content of the wood (7% to 12%, for example, or whatever may be specified) is attained. Thereupon the throttling valve 27 is closed and valves 33 and 88 are opened, dumping the entire liquid contents of the retort and pipe 59 into the treating drop tank 85. a r l When the retort is completely drained of treating ysolu-v tion valves 33 and 34 willbe closed, sealing oi the retort. Thereafter, valve 88 in line 89 will be opened `to connect the rbottom of the retort and as they are drawn out by the vacuum pump and condensed a substantial sub-atmospheric pressure develops in the retort, lowering-the azeotrope boiling point below 190 F. and effectively the bottom of the retort through pipes 31, 59 and y 89 tol Y a suitably cooled pre-cooler and pre-condenser 91 and wet vacuum pump 92. Liquid pump 93 will be started to supply a suitable seal liquid such as solvent from'pipe 93a and tank 53 to the wet vacuum pumpY 92, this latter pump discharging directly to condenser 41. 1

When vacuum is being applied to. the retort, the wood still retains a temperature in the neighborhood of 190 F.

or higher, resulting from previous heating. The residual heat in the wood will supply the heat necessary for evaporating the -azeotrope vapor formed by residual moisture and residual solvent in the wood. Enough vacuum should be applied to reduce the boiling point of the moisture and solvent far enough below the temperature of the Wood so that said residual heat will be adequate.

The solvent vapors, then in the retort, are relatively heavy vapors hence are advantageously withdrawn from bedried bone dry.

The evacuationof azeotrope and solvent vapors may,`

aiding Ythe stripping of solvent from the wood.

The moisture still remaining in the wood a1ds'g`reatly-` in' thesolvent stripping, while solvent remains to be stripped, hence prior to this time the wood should not be aided by admitting steam through valve 94 to help force the other vapors through the bottom of the retort. Additionally, as a further aid to solvent stripping and with some woods to add moisture to the wood to equalize stresses and prevent case hardening, the vacuum valve 88 may be closed for a time to enable steam'pressure to build up in the retort. Whether ornot such steam pressure is created, and usually it is advantageous to do so,- afnal vacuumw'ill be pulled on the retort through opened valvey 88,-the stripping steam will be shut off and when theV wood is stripped of solvent a vent valve 9S-will`bev opened admitting air to restore atmospheric pressure to the interior of the retort soA that the retort door may be opened.

AAlternatively, when the Vretort has been drained and beforeY treating solvent is added, in view of the fact that azeotrope vapor still remains within the hot wood, the mere introduction of treating solvent at a temperayturesu'bstantially below the' azeotrope boiling point will cause vthese vapors to condense inthe wood and thusv the treating solvent is drawn into the wood withoutthe aid of especially created pressure. Under these circumstances the above mentioned short evaporation period, the closing of the vapor 34 and the subsequent development of pressure in the retort become unnecessary.

The use of one solvent bath for drying and a second1 bath for treating, as above described, constitute the proper procedure whenever the Wood contains resins which could become dissolved into-the solvent duringl drying. If, however, the wood being dried contains noresin, or other such eXtractives, and is to be treated withV an impregnating additive, such additive mayfbe in`v corporated inthe originalV solvent bath at the start of -the drying operation, as such! a bath will not be con.

taminated by resins and may be re-u'sed.

The wood, substantially free of resins, if it originally contained resins, and dried to the desired nal moisture content and impregnated with the selected additive or additives may now be removed from the retort.

During the stripping action the solvent in the treating solution is removed from the interior of the wood as a vapor, hence the additive which the solvent carried into the Wood remains in the wood, intimately and thoroughly dispersedtherein. v

As heretofore stated, the solvent received into drop tank will contain resins extracted from resinous type woods. These resins can be valuable byproducts of the process.

cade typek having AWeirs `such as 108 over which the solu-` tion` may flow as steam coils or othersuitable heatingV means (not shown) evaporates the solvent as a solvent vapor therefrom. Another similar still 109 is connected in series as shown and the-solvent vapor from .both may r be delivered by pipes 111, 112 and 113 to the condenser 41, whose functioning has been described heretofor.

The resin concentrate, more or less free .of solvent,

may be delivered by pipe 114 into a ring-packed column 115 of conventional type to be finally stripped of solvent by means of steam in an obvious manner. The solvent- If their concentration is not deemed tooV great inany given batch o'f solvent, the solvent may be Whenever the resin concentration warrants'it free resin may then be pumped by pump 116 to the st orage tank 117 while the solvent and steam as an azeotrope vapor is Vdelivered by pipes 118, 111 andg113 to condenser 41.

lIf both absorbers 46 and 47 have been in use and become solvent saturated they may be regenerated by opening valves 120 and 121 which will admit stripping,

126 through line 127 into the pipe v113 for delivery to thel condenser 41. l

'A The automatic' control The,inven'tion comprehends vautomatic control of the process steps, and employs apparatus which is in part timerffcontrolled and in part Yresponsive to conditions which develop in the process. A schematic diagram of the control apparatus is shown in Figures 3 and 4 and its manner ofuse will now be explained. y

The electrical circuit shown in Figure 3 `is supplied with electric current from a suitable source at 1 l0-volts and 60 cycles, for example, as represented by the power wires -131wand 132. The automaticvalves hereinafter mentioned are generally large in a commercial plant and preferably are opened by air powered mechanism of conventional nature, and preferably are so arranged and designed as to be normally closed, for example by springs, in the absence of processtoperation or whenever there is a power or air failure. Compressed air Vfor opening these valves may conveniently besupplied, as shown, by solenoidfoperated valves (under control of the electrical crcuit). The details of construction of these conventional valves do `not constitute a part of -this invention, hence are not shown.

,The-electrical circuit includes one hand-operated switch, one d oor-operatedl switch, two switches responsive to-the azeotrope vapor pressure occurring during the evaporation of moisture, several motor-operated timers which cause cam-operated switches to openl or close, and al Closing of the hand-operated switch.

number of relays. initiates a cycle of operations which are thereafter automatically controlledand which terminate when the charge of lumber in the retort has been .dried and treated and is ready for removal. e 1

lThe retort 11, in which one or more carloads of lumber may be placed at a time for treatment in accordance with this invention, is a well reinforced steel chamber provided with a door (not shown) which can betightly sealedrto retain the liquid solvent employed to submerge the lumber. There is shown in the circuit diagram in Figure 3 a door limit switch 133 of any suitable construction, the details of which do not constitute a part of this invention, but which will remain open -until the door is closed.

Assuming that the retort has been loaded with lumber and the door limit switch' 133 is closed and all ofthe apparatus is in condition for the beginning of a cycle of' process steps, the operator will then close thestart-stop button .134 which will supply current to relay 1R` in Fig.` 3, which upon being energized will close the `normally open relay contact 1R1 and normally open relay contact 1K2 thus supplying voltage to the bus bars or wires 135 and 136 extending vertically in Figure 3 -and also'at the same time supplying voltage to the bus bars or wires 137y and 138 of Figure 4, which may be considered a continuation of wires 135 and 136 of Figure 3. When voltage is thus supplied to the wires 135 and 136timer motors 1T, 2T and 3T are energized.

Drying Timer 1T, when it begins to operate, maintainsva circuit from wire,136 through normally closed switch 4R21,

' vmined level, which preferably'is about four inches above the top of the wood containedV in the retort and su'icient 12 through the upper closed contact 139 of the timer switch 1T1 (Figf3) lthrough the coil of a solenoid-operated air valve 1141 which'controls the supply of compressed air; tO `open-and hold open the overhead raw solvent supply` valve 58. Valve 58 supplies solvent to the retort until the lumber-is submerged or nearly submerged; whereafter timer 1T, Whose cycle is adjustable and may be of about Siminutes, operates switch 1T1 at the end of its cycle to cut off current `to'solenoid of valve 141 and supply current :through its lower contact 142 to the coil of solenoid Y valve 143'which supplies compressed air to open and hold open the throttling valve 27, which admits enough Vsolvent to the retort to `keep the lumber submerged and the liquid level .in .the retort high enough vto continuously overilow rthe/baffles 23. The overhead solvent supply valves 58, 27 vand'87 are controlled not only during the`sequence of operations now being described but are also subject to control by the liquid level control device 24 (see Fig. 5) so that kthe solventv in the retortem'ay'n'ever rise above la predeterto overflow the bales 23. l

As shown in Fig. 5,'when the liquid level is below the desired level the rfloat element suspended on the pivoted `lloat arm v14.4 rotates a apper 144atoward aBourdon tube 145. In a manner hereinafter explained, this movementrcauses airrto be supplied to the solenoid operated valves 141, 143 and 148 adequate, if any one of them l be open, to actua'te their respectively associatedY valves 58, 27-and 87 fto full open position. However, when the liquid level in the retort Vreaches vthe desired predetermined levelth'e ycooperative action of the float and associated' mechanism reduces this air supply pressure to such an extent that none of the valve 58, 27, or 87 can be actuated to open position even if their associated control valves be open. Air actuated valves of this type, which are airactuated to open position against spring pressure,

are wellV known, and customarily they have suitable bleed v v ports or the equivalent so that if they be ydeprived of actu-V` ating air pressure their springs will close them.

When voltage has been applied initially on the closing y v of-the startgstopbutton v134, current is supplied through the coil of-the solenoid-operated air valve 149 from Wire'V 135 through the lcoil through normally closed switch SR1 of relay SR and normally closed switch 2R2 of the relay 2R to the wire 136. When valve 149 is thus operated it A' supplies compressed air to open the vapor valve 34 so that air and vapors may flow from the retort. Compressed air supply pipes connected'with the various valves are not shown in the drawings, except inFig. 5.

ATimer 2T, also now operating,' serves to delay the opening ofthe retort steam valve l63 until liquid solvent entering' the retort at the start of operations has lled the retort to, or lpartly to, the desired maximum level or at least has covered the steam coils. Hence, the switch ZTI is normally open asshown `in Figf3 ybut closes after a predetermined short interval when timer 2T completes,

its cycle, establishing circuits from wire r through the coils of the solenoid-controlled air valves 151'and 152 V*through then closed switch `2T1 and normally closed switch 14R1 of relay 14R. The/valve 151 thensupplies compressed air to openthe' retort steam valve 63 to admit'steam to the coils in the retort for; heating the solvent, while valve 152 `supplies airt'oropen thesteam condensate drain valve 64. Usually y about twoV minutes after the solvent begins to flow into the retort. it is appropriate to admit steam.

Timer 3T, also now operating, has the functionof pre-- .venting the intermediate vapor flows'witch A153 asso-v `ciated with the vapor ow meter from exercising any control over the operations untilswitch 3T1 of timer 3T is closed. When the timer 3T runs for its set time cycle andy closes switch 3T1l there will be a suliicient amount of 1 13 vapor passing through the retort vapor linev 35 to prevent the intermediate vapor flow switch 153 from closing. t

. Duringthis period the solvent bath becomes heated by the steam coils to well above the azeotrope boiling point, preferably in the range of 210 to 240 F., and moisture is being removed from the wood as a part ofthe azeotrope vapor. This drying period continues until itis terminated by the vapor flow meter actuating the intermediate vapor flow switch 153. This period will usually require several hours, dependent upon the nature of the wood being dried and the dimensions of the wood, thicker pieces requiring more time than thin ones.v

Soaking Later when the vapor llowr through the orice plate 77 drops to the point where the intermediate vapor switch 153 can close, voltage will then b e impressed from wire 135 through the vapor ow switch 153 and timer switch 3T1 and the coils of the 2R and 14R relays to wire 136. When relay 2R becomes energized all of the switches on this relay are operated and switch 2R1 closes, establishing thereby a holding circuit for relays 2R and 14R directly between wires 135 and 136, making them no longer dependent on vapor llow switch 153 for current.

When relay 2R is energized switch 2R2 opens cutting off current from solenoid-operated valve 149, thus' cutting off air from vapor valve 34, which closes. Relay 14R, now energized, opens switch 14R1, thus cutting o current from air valves 151 and 152 which close and respectively cause the retort steam valve 63 and condensate valve 64 to close. The residual heat in the solvent bath and in the heavy steel walls of the retort will cause azeotrope vapor to evolve in the retort a few minutes until the vapor becomes superheate'd and imposes such pressure on the wood as to cause condensation of the vapors therein, allowing the solvent to penetrate it and initiate the soaking period. Should the retort pressure exceed a predetermined flgure the safety relief valve 154 in by-pass 155 will relieve the pressure.

Voltage will also pass from wire 135 through the normally open but now closed switch 2R3, through the motor of timer 5T to wire 136. This starts timer 5T operating, which controls the length of the raw solvent soaking period. This timer 5T is adjustable and its cycle will usually be set to allow about half an hour or a little more for each inch of thickness of the lumber to be soaked.

The length of the soaking period is automatically terminated by the timer 5T which at the end of its cycle causes switch ST1 to close and thus to supply current from'wire 135 through the normally open but now closed switch 2R1 and switch 5T1 (now closed) through the motor to timer 6T to wire 136.

Drying resumed Switch ST1, when closed also supplies `current through relay 13R to energize it whereupon switch 13R1, which is normally open, but which now becomes closed, establishes a circuit from wire 136 through normally closed switch 16R2 through 13R1, through SR1 (normally closed) and the solenoid of valve 149 to wire 135.

Thus when voltage is supplied to the control valve 149 for vapor/valve 34, the latter opens relieving pressure in the retort and enabling the azeotrope vapors therein to resume flowing to the condenser 41.

The closing of switch ST1, at the end of the soaking period, also closes a circuit from wire 135, through closed switch 2R4, closed switch ST1 and relay 3R to wire 136. When relay 3R is thus energized switch 3R1 closes establishing a circuit from wire 136, normally closed switch 4R1, switch 3R1, closed switch 2T1, and the coils of air controlvalves 151 and 152 to wire 135, thus reopening the steamsupply valve 63 and condensate valve 64 to supply heat to the solvent for further drying.

Dralining of retort Timer 6T, which was started at the end ofthe cycle oi timer 5T, limits the duration of the heating period after the soaking period, by closing switchk 6T1at the end ofV its cycle thuspsimultaneously energizing relay 4R, the motor of timer 7T and through normally closed switch 7T1 energizing the solenoid' of air control valveV 156 which supplies air pressure to open the raw lsolvent drain valve 32. When relay 4R becomes energized the normally closed switch 4R2 (shown near the top of Fig. 3) opens, which action cuts off the supply of current to the air control valve 143 for the raw solvent throttling valve 27, closing both valves. The raw ysolvent drain valve 32, nowbeing open, enables the solvent" in the yretort to drain into the raw solvent drop tank 80.' Also the energizing of relay 4R causespthe normally'closed switch 4R1 to open, cutting off the supply of current to the control valves 151 and 152 for the retort steam and condensate valves, respectively, thus allowing these valves to close.

. Treating Timer 7T controls the length of time the raw solvent drain valve will be open. When the motor of the timer 7T completes its cycle at the end of such period/of'time as isrequired for draining the raw solvent, timer 7T then operates timer switch 7T1 de-energizing valve 156, closing valve 32 and supplying current to the relayV 12R (Fig. 3), to timers 4T and 8T and to the'air control Valve switches 16R3-12R1-2T1, and solenoids ofvalves 151V and 152 to eiect the opening of steam valve 63 and condensate valve 64. The treating solvent entering the retort is thus heated and the vapor valve 34 beingopen evaporation of moisture from the wood is resumed when the temperature rises above the azeotrope boiling point.

Timer 8T functions to control the length of time the overhead treating solvent valve shall remain open, this time being the amount of time required to supply treating solution to the retort to submerge the lumber therein and to cause the solvent to approach or attain a level high enough to overtlow batlles 23.

When this period has concluded timer 8T shifts the switch RT1 from the position shown in Fig. 3 where it is shownsupplying current to the control valve 148 for the treating valve 87 downwardly to its lower contact where it supplies current through wire 157 to control valve 143 which supplies air under pressure to the raw solvent throttling valve 27, which serves as before to rriaintainv the solvent level in the retort during this drying period.

Treating solvent soak At the same time closed switch 16R2 opens and thus cuts4 off current from the control valve 149 which will cause vapor valve 34 to close. Thereupon the vapor will be retained in the retort and will become superheated by residual heat in the retort and its contents enough to.

create pressure enough to cause vapors in the wood to condense, whereupon the solvent containing the treating additive or additives begins 'to vsoak into the Wood. Thus timer 4T initiates the'tre'ating'solvent soaking period.

` In laddition to initiating the treating solvent soaking period vtimer: 4T also, while it is still running its cycle, not only serves to postpone the energizing of relay 16R but also the energizing of timer 9T. When the latter is energized its cycle begins at the beginning of the soaking period and terminates at the end'of the soaking period at which time it causes normallyopened switch 9T1 (top of Fig. 4) to close, thus supplying current to relays 5R and 15R. When 5Rv is energized switch SR1 closes and supplies current fromwire 136 through normally closed switch 9R1 to control valves 151 and 152 which open the f steam valve 63 and the condensate`valve'64. At the same time when relay 15R-operates it closes switch 15R1 (Fig. 3) and supplies currenfthr'ough normally closed switch SR1 to control valve- 149, thus causing vapor valve 34 to open. At this time evaporation of further moisture from the wood resumes.

Normally open switch SR2 (Fig. 4) also is closed by relay 5R and suppliescurrent to the timer 10T. Timer T during its cycle continues to hold open the circuit through the minimum vapor flow switch 158, the timer operated switch 10T1 then being normally open. When treating southern yellow pine lumber one inchl inthickness the cycle oftimer 10T will be somewhat lessV than an hour. v l

Subsequently, when timer 10T closes the switch 10T 1 and the minimum vapor flow meter switch 158 Vbecomes closed by the effect of a small vaporrflow, a circuit is then established through relay 6R (top of Fig. 4) closing normally open switch 6R1 establishing a holding circuit for relay 6R. The closing of switch 6R2 when relay 6R is energized establishes a circuit through .the motor of timer 11T.

Timer 11T establishes a time delay between .the Iactual closing of the minimum vapor flow switchf158 and the opening of the treating solvent drain valve. Experience hasshown that the vapor flow at or about the time when control is desired by the minimum vapor flow is insuicient, with present available equipment, for controlling with eXtreme accuracy the time when the retort should be drained. Hence, the minimum vapor flow switch is allowed to operate at asomewhat higher pressuresuch ascan be relied upon to give consistently a fairly accurate indication of the amount of vapor flowing, after which the evaporation of azeotrope vapor is continued under control of timer 11T for a predetermined period before the drain valve is opened. Such a delay period is subject to variation and in the handling of certain kinds of wood such as southern yellow pine may be approximately one hour. When switch 11T1 (Fig. 4) is closed at the end of the cycle of timer 11T, the relay 7R (Fig. 4) becomes energized. Normally closed` switch 7R1 (Fig. 3) is know opened, cuttingoi vcurrent through wire 157 to valve 143,1 thus causing the solvent throttling valve 27 to close. The energizing of relay 7k also closes switch 7R2, thus supplying current to the control valve 159 which supplies compressed air for opening the treating solvent Vdrain valve 33 shown in Figure l, thus draining the retort.

Simultaneously with the opening of the treating solvent drain valve 33, the now closed switch 7R2 closes a circuit through the upper'closed switch contact 161 of timer switch 13T1 and 10R1 and the coil of the solenoid oper-- 'ated valve 162 supplying air pressure to open vacuum valve S8 so that pipe line 59 may be drained while valve 33 is open. l

The closing of switch 7K2 also supplies current to the motor of timer 12T, which functions to control the amount Vof time the treating solvent drain valve 33 shall thereafter be open. As soon as timer 12T closes switch 12T1 a circuit is then established through relay 8R which upon being energized opens the normally closed switches lSR1 (Fig.V 3) and SR2 (Fig. 4). Switch SR1 upon being open removes voltage from the control valve 149 so that the vapor valve 34 'will' close. 'Switch SR2' upon'being opened removes voltage from ythe control valve 166 which controls the treating solvent drain valve 33, closing the latter.

When timer 11T closed switch 11T1 and energized relay V'7R and rthereby closed switch 7R2, as stated above, a circuit is likewise established throughthemotor of timer 13T, starting .that timer to operate, and vwhich through the upper switch -contact 161 of v'switch `13T1 controls the length of time the solenoid 162 shall remain energized and hence'the length of time the vacuum' valve 88 shall remaink open. f

When the retort has beenV drained and the relay SR has been energized, the normally open switch 8R3 (Fig. 4) being closed establishes a circuitbetween wire 137 and 138 through the motors -of timers 14T, 15T, 16T and 17T, thus simultaneously starting these timers. At

the same time currentA is supplied through the then closed` switch 14T1 and the closed switch 10R2 vsimultaneously to the solenoid' operated'switch 163 which fstarts the.` vacuum pump '92'shown near the top of Fig. 1. At the same time solenoid operated switch y164 is energized to start the liquid seal pump 93. ,l

Timer 14T controls the length of time that the vacuum pump 92 and the seal liquid pump 93 shall operate.

At this point inthe cycle of operations all of the valves in the system are closedwith the exceptionof the vacuum valve 8,8 and the retort steam supply valve.

As soon as timer ,15T reaches the end of its cycle, switch 15T1 closes, voltage is impressed through normally closed switch 11R1 (Fig.V 4) Vthrough a control valve 165 which supplies compressed air tol open a retort steam fitting valve 94 (Fig: 2) allowing stripping steamto enter the retort. ,Y

When timer 16T reachesthe'end V`of* its cycle, switch 16T1 closes and relay 10R (Fig. 4) becomes energized,

which removes voltage from control valve 162, closing,

the vacuum valve 88. Normally closed switchV 10R2 likewise opens, deenergizing solenoids 163 andl64 which then stop vacuum pump 92 and seal pump 93.

' After vacuum valve 88 is closed, stripping steam continues to be fed into the retort to build up positive steam pressure therein. When timer 17T reaches the end of its cycle, Vswitch 17T1 closes and 11R becomes energized, opening normally closed switch 11R1, which de-energizes the 'retort steam stripping control valve 165 and also closes normally open switchY 1,1R2, whichreenergizes vacuum control fvalve 162 toopen vacuum valve 88 and switch 11R3 closes to supply current to solenoid 163 to actuate vacuum pump 92 and' solenoid 164 to actuate seal pump 93 so that vacuum againvi's pulled on the retort.y

When timer 13T reaches the endv of its cycle, the switch 13T1 is actuated to de-energize solenoid 162, closing vacuum valve 88 and to transfer power through its lower switch contact 166 to a circuit leading through motor of timer 18T, starting the latter, and supplying voltagealsoto relay 9R. When relay 9R is energized switch 9R1 (Fig. 3) normally closed, now opens cutting off voltage lto the retort stream supply control valve 151 and condensate control valve 152.

When 14T finishes its cycle switch 14T1opens, deenergizing solenoids 163 and 164, stopping/the vacuum pump 92 and seal pump 93.l

Current through the upper contact of timer switch 18T1-energizes solenoid controlled valve 167, which supplies air to `open and hold open-the vent valve (Figs. l and 2) admitting air into the retort to raise .the Ypressure to atmospheric so that the d oor may easily be opened. At the`end 'of timer 18Ts cycle, switch`18T1 moves to its lower contact tosupply current to the coil of a warning horn 168, signifying that the wood is ready for removal from `the retort. The start-stop button is marmally put in stop position and opening of the 17 door will open the door limit switch, and automatically the electrical circuits will be restored to original starting position.

The following are the approximate time cycles set on the various timers for 2" thick dimension southern yellow pme:

The details of construction of the timer mechanisms above referred to do not constitute a part of the invention. While other suitable timers may be employed, timers manufactured by the R. W. Cramer Company of Centerbrook, Conn., have been used satisfactorily herein. As indicated in this specification, their motors are started by current supplied through control contacts in the circuits of Figs. 3 and 4 to initiate their individual timing intervals. At the end of such interval each timer operates a switch in the load circuit, for example, see 12T,

or 13T, in Fig. 4, and the timer maintains this condition until the control contact is broken, which would occur here when either switch 133 or 134 is opened. These timers, for example, Cramer type TEC, then automatically reset themselves to repeat their operation when again required to do so. The interval of each timer may be adjusted manually within its individual design limits, hence an operator may make substantial variations in the time limits of the various steps of the process.

Vapor flow meter and switches In Figure 1 there is shown an orifice device 77 interposed in the vapor iiow pipe 35, and in the electrical circuits of Figures 3 and 4 there are shown in circuit an intermediate vapor llow switch 153 and a minimum vapor ow switch 158. These devices and their functioning will now be further described in connection with Figures 6, 7 and 8.

The oriiice device which is shown schematically in Figure 6 consists of a plate 171 clamped between two anges 172 and 173 interposed in the vapor ilow pipe 35. The plate has an orifice 174 having a diameter smaller than the pipe diameter.

In the assembly there is provided a duct 175 on the high pressure side of the orice plate connected by pipe 176 to the high pressure chamber 177 of a Barton No. 211 differential flow meter, generally indicated as 178, `and schematically illustrated in Figure 6. Another duct 179 communicating with the face of the low pressure side of the oriiice plate is connected by pipe 181 to the low pressure chamber 182 of the same meter.

As this Barton meter manufactured by Barton Instrument Corporation of Los Angeles, California, is a wellknown commercially available device and as its construc-v tion is not a part of this invention it is not illustrated herein in detail, vbut is illustrated schematically. It will sulice here to state that the low pressure bellows 183 has its movable end operatively connected by a rod or shaft 18 184 to the movable end of the high pressure bellows 1 85, which shaft is subject to pressure from an adjustablevcompression spring 186. A follower arm 187 fixed on a torque .shaft 188 is urged byY a suitable spring (not shown) to maintain contact with a collar 189 fixed on rod 184. Diierential pressure impressed on the bellows effects reciprocation of rod 184, which is utilized to oscillatean indicating pointer (not shown) and the two switch actuating arms 191 and 192 which are iixedly mounted on the torque shaft 188 at a'point somewhat removed from the arm 187.

A bell crank level pivoted at 193, generally indicated as 194, has relatively `angularly adjustable arms 195 and 196, the upper one maintaining constant contact with" actuator arm 191, the lower, 196, carrying a magnet v197, such as an alnico magnet. As shown in Figure 7,

wherein the actuator arms occupy the angular position which they have at zero flow position, this magnet is close enough to the fixed position of the non-tilting mercury switch tube 198 to attract-a responsive magnet 199 ixed on the wire 201 and swing the wire 201 about its coiled spring portion 201 into the mercury pool 200 in the bottom of the tube to close an electric circuit therethrough to wire 202, the latter being permanently in contact with the pool. This is the minimum Vapor flow switch 158 schematically and more simply shown in Figure 4.

When the vapor ow through the orice is substantially higher than the flow which has been selected to constitute the minimum set point, which might be about 250 cubic feet per minute, for example, the diierential pressure action of the vapor ow meter will have the arms.

191 and 192 in an angular position enough degrees counter-clockwise from the position shown in Figure 7 to have moved the magnet 197 clockwise far enough so that its magnetic eld no longer will hold magnet 199 in opposition to the pull of its associated spring 201' and the spring loaded wire 201 will spring out of the mercury spring 204', which tends normally to close the intermediate vapor ow switch 153.

Figure 7 shows a normally closed circuit in tube 205, which is switch 153. Figure 8 shows magnet 208 responding `to magnet 206 and the intermediate vapor liow switch 153 is open. Torsion springs (not shown) acting on the pivoted bell cranks 194 and 207 about their axes cause them to maintain constant contact with their respective actuating arms 191 and 192.

It should be understood that in the early stage of the.

wood drying the vapor flow will be much in excess of the vapor flow measured at the intermediate control point. While the vapor ow meter is moving up to and past the mtermediate point the timer system will keep this meter out of the circuit, henceit can have no operating control on the process.

The intermediate vapor ow switch 153, in actual use, is adjusted so that when the vapor flow. diminishes to a desired predetermined vapor ow, which might be 600 cubic feet per minute of vapor flow, for example, the magnet 206 will become rotated far enough 'counterclockwise to release magnet'208 and allow this switch' to close.

Retort solvent level control which is shown diagrammaticallyrin Fig.v 5 works satisfactorily and its coordination with other parts of the invention will now be described.

.The apparatus shown in Fig. 5, with the exception of the solenoid operated valves 141, 143` andV 148 andthe an operated valves'associated therewith and the connections thereto, is manufactured by Fisher Governor Com pany of Marshalltown, Iowa. This Fisher equipment includes a filter tank 211 into which air is supplied through the tube 212 from an air pressure supply line, the air passing through a filter 213 past a manually adjustable valve 214, thence by pipe 215 into a double diaphragm assembly generally designated as 216. This air enters a chamber 217 rand ows past the spring loaded valve 218 intov the chamber 219, whenever valve 218 is open.

VPart of the air admitted into the chamber 219 then owsthrough pipes 220 and 221 into pipe 222 which supplles alr to4 the control valves 141- and 148, and through pipe, 223 to supply air to the control valvev 143.

LvSome of the air entering through pipe 215 rises through duct 224and bleeds through a small orifice shown-near the outlet o f ducty 224 into' the upper chamber 225V and thence ows throughpipe 226 through the central duct 227 shown in the BourdonV tube 145 and emergesV through a nozzle opening in the end of the tube adjacent the opper144a, at a rate of oW equal to the rate of flow through said orice, unless the nozzle opening is restricted by the apper ,14411. The apper 1445: is xed on the same pivotedshaft 1441) as is the iioat arm 144, hence the position of the float element 26 is one factor in determining whether the flapper restricts the tube nozzle. When the nozzle opening is unrestricted by the flapper the pressure in 'the upper chamber will be zero. Another factor depends on the pressure applied tothe outer duct 228 in the Bourdon tube bymeans of air supplied through pipe 229 past .the manually adjustable double ended valve 231 into the pipe 232. Valve 231 is employed to proportion the amount of air allowed to flow to pipe 232 or through the bleed port 233. Increased air pressure supplied by pipe 232 willA tend to straighten the Bourdon tube, thus beinga factor in the spacing between the liapper and the tube end, which atfords a means of varying the maximum liquid' level in the'l retort. i'

The lower diaphrarn 234 and the upper diaphram 23S,

` together with spring 236, suspend the central unit 237 sothat it functions as a lloating valve seat in respect to the valve 238. When this value seat'presses down far enough on valve 238 thisrmovement not only closes valve 238 but unseats valve 218, against the action of spring 239, which conditionv is shown in Fig'. 5.

The valves 58 and 87 are largecapacity valves'to permit rapid iilling of the retort 11, Subject to the 'control of their associated solenoid operated rvalves 141 and 14S they are actuated toward open position in opposition to conventional springs (not shown) if the air supplied to them exceeds a certain predetermined pressure. The other valve 27 in the by-pass aroundvalve 58 is arsmaller valve having preferably a weaker vspring and may be opened by air pressure which is insufiicient to open valves 58 or 87.

j When the retort 11 is being iilled, for example, by solventsupplied through valve 58, and oat 26 is below the f illed level, apper 144a restricts the escape of air from the Bourdon tube. Thus air pressure-accumulates and is retained in upper chamber 225 suiiicient to force unit 237 downwardly,` closing valve 238 and holding valve 218 open, whereby enough of the line pressure in pipe 215 will be impressed through pipe 221 and 222 to hold valve`58 open.

vrShould the retort solvent level/reach a predetermined level at or close to the desired lled level before timer 1T has completed its cycle and has actuated switch 1T, to deenergize solenoid operated valve 141 and thus cause valve 58 to close, the liquid level control itself will operate to close valve 58, as follows.

t When the liquid level rises in the lretort high enough to cause apper '14421 to moveV away from 'theen'd of the Bourdon tube 145, air will escape more rapidly from the central Yduct ,227. and thus,r the pressure in'I the upperr: chamber 225 will decrease. The central unit`237` inithei diaphragm' assembly will be raised byl springv 236y and" by the airpressure in chamber 219 until valve' 218 closes" When timer 1T, in this example, completes its' cycleV switch 1T1 will shift, de-energizing valve 141 andenergizf ing valve 143, whereafter should the air pressure supplied by lines 221 and 223 through the now open'valve 143 be great enough it will open valve 27 and throttle it toA supply solvent to the retort just rapidly enough to oiset solvent loss' from the retort and maintain the desired liquid level therein. v

It will now be perceived that whenever the solvent level drops', due to evaporation or other causes, the-dapper will approach the endwof -the Bourdon tube and diminish the 'ow of escaping air. This will cause air pressure in chamber 225 to increase forcingnthe floating valve seat down until it pushes downon valve 238, stopping the wasting of air past that valve and unseating valve -218 and restoringair pressure to-chamber 219 and pipe 221 which if suflicient will reopen or further open any air operated solvent supply valve whose associated solenoid operatedcontrol valve is open at the time, thus to increase or restoreV solvent flow to the retort.` During a drying period it would be the throttling valve 27 which would thus be regulated by the diaphragm assembly. Y t

Variations in air pressure transmitted tokpipc 232 will cause the Bourdon tube to distend or contract, thus varying the maximum level in retort Within desirable or per-Y missible certain limits controllable by valve 231. e Y

It has been mentioned in the foregoing description that the rate of azeotrope vapor ow in the retort diminishes noticeably as the instant moisture content -o'f the wood approaches the critical moisture content.v This .diminution is readily detectable when `the moisture co-ntent has dropped to the neighborhood of 50% or Athereabouts. Soaking at this time before further drying. has appreciable advantages. Instead of directly measuring the' vapor flow by means of the variations in pressure thereof I might determine the rate of azeotrope vapor evolution or flow at a selected interval of time by measuring the condensate derived from this vapor in such period of time, measuring either the water condensate or vthe solvent condensate or both together. The measurement thus taken, either of rate of ow, or volume or weight of the condensate, could be used to indicate to the operator when .the drying operation should be' interrupted and the soaking step initiated. Also at a .later Vinterval similar information could be utilized to determine when to terminate the drying and treating operation. Instead of merely indicatingto the operator when to'im'tiate these changes, automatic Vcontrol could be provided automatically responsive to the measurement of the condensate.

As steam furnishes the heat for the azeotrope vapor evolution in the retort, it will be recognized that the rate of steam consumption will vary'in proportion to the. rate of azeotrope vapor evolution. vAccordingly-as an alternative control method, I might measure eithery the ilow of steam into the coils 21 or the steam condensate emerging therefrom Vby conventional flow measuring devices fand' regulate the soaking and drying vperiods by correlating such Ydevices with thecontrol circuits in accordance with the same principlesgoverning the use of the Bartoniiow meter. f v

-In the event that the azeotrope vapor condensate is tobe measured, as suggested above, vto vdetermine when to begin soaking the wood-and when to terminate dryingrof the wood in the solvent bath, it would be preferable to measure the combined condensate beforeV gravity separaf OI; of 111,19 SlYilfnd water; In such case va separate 21 condenser would be added to receive and condense va.- pors from pipe 113 and discharge them into the separator 42, so that the condenser 41 would then receive vapor only from the retort. I y

While some other suitable apparatus couldl be used, I have shown diagrammatically in Fig. 9 apparatus which could be used and would be responsive to the rate of ow of azeotrope vapor condensate. The condensate of intermingled solvent and water, instead of discharging directly to gravity separator 42, as in Fig. 1, would as shown in Fig. 9, drain from condenser 41 through pipe 245 into a sealed chamber 246 and fall into the cup 247 fixed on arm 248 pivoted at 249, having a suitable counterweight 251. When the condensate flow exceeds a predetermined intermediate rate of flow, as Ait Iwould in the early stages of wood drying, the drain stem 252 would not drain the cup as rapidly as it was being filled and the cup would be held in the downwardly tilted position shown in Fig. 9, resting on a support bracket 253. The condensate overowing the cup 247 would spill into the lower cup 254 pivotally supported at 255 on arm 256 and having a. `suitable counterweight 257. The drain stem 258 of the lower cup will be gauged to drain at-a predetermined rate which may, for example, correspond to the Vapor condensed at the same vapor flow rate which enables the minimum vapor flow switch 158 of Fig. 4 to close. Condensate in excess of that rate would ilood the lower cup and hold it down against the support bracket 259, the excess overowing into the bottom of the tank and then draining into a pipe such as 68 for delivery to the gravity separator 42.

The drain stem 252 of the upper cup may be gauged to drain condensate at a predetermined rate such as, for example, the amount that would be condensed at the vapor flow rate which enables the intermediate vapor iiow switch 153 of Fig. 3 to close. When this rate is reached in the drying process and the upper cup drains it will be tilted up by its counterweight and the arm 248 will contact and close a suitable switch 261 which would take the place of switch 153 in the circuit of Fig. 3.

Later in the drying and treating process, when the flow of azeotrope vapor condensate drops enough so that the lower cup will cease flooding and will drain, the arm 256 aiiixed to that cup will be tilted to close a suitable switch 262, which would take the place of the minimum Vapor flow switch 158 of Fig. 4. The drain stems of these two cups could be regulatable or replaceable to cause these cups to tilt upwardly after any selected iiow rates of condensate had been attained. Thus the devices of Fig. 9 could be utilized with the control circuits of Figs. 3 and 4 for the same general control purposes.

In the event that it may be desired to evaporate moisture from the wood under suicient vacuum to lower the azeotrope boiling point very substantially below 190 F., the boiling point of the perchlorethylene-water azeotrope, I may, as said before, interpose a motor driven vacuum pump 263 between the condenser 41 and the gravity separator 42. When this pump 263 is so interposed there will also be provided a by-pass 264 around the pump and in the by-pass a check Valve 265 opening toward the separator 42. The motor of this vacuum pump will then be energized under control of an automatically operated switch (not shown) connected tothe control circuit whenever the vapor valve 34 is opened and will be de-energized whenever valve 34 is closed.

When the pump is stopped condensate from condenser 41 may iiow to the separator through the by-pass. The check valve 265 will be closed by suction exerted on it whenever pump 263 is operating.

Whenever azeotrope vapor has been removed from the retort 11 at .a pressure lower than would or could later conveniently be exerted by the solvent stripping vacuum pump 92 it would be advisable and preferable to allow or cause the wood to become heated to a temperature considerably above the azeotropic boiling .point which would be determined by the suction eiect of pump 9.2;v before 'that pump is put into operation. This :could be" accomplished by shutting off the Vacuum pump 263V shortly before the retort is drained, and allowing the' solvent bathl to heat the wood to the desired extent abovel the last mentioned boiling point. Heat could be sup'- plied to the wood otherwise, as by steaming, if desired.l

Whatever the temperature and pressure in the retort may be during the -drying or impregnation steps, there `should be enough superheat in the wood during the stripping step to supply the necessary latent heat of evapora-v tion to the solvent being stripped. If the considerable mass of metal in the retort be at this time above the azeotrope boiling point during the stripping step this heat will be of assistance. p

Furthermore, when the stripping step is commenced there should remain in the wood more than enough moisture from which to form azeotrope vapor with all of the solvent then present in the wood. Thus all of the solvent may economically be stripped from the wood, to avoid solvent losses in the process. The use of steam to supply such moisture, in part, is possible but is less economical.

While the solvent frequently referred to herein is the non-flammable, water-immiscible perchlorethylene, other non-flammable, water-immiscible chlorinated and lhalogenated hydrocarbon solvents, including fluorinated hydrocarbons, may be substituted therefor, provided their lphysical characteristics are suited to the purposes of this invention and the cost of employing them is found to be economical. Such desirable solvents are non-flammable and have a constant azeotrope boiling Ipoint. The choice of solvent may vary in accordance with availability and price, and the various particular operating conditions under which it is desirable or feasible to dry or otherwise treat a particular type of wood.

Among the various chlorinated hydrocarbons `which may be employed are perchlorethylerie and trichlorethylene. Of these perchlorethylene is preferred. Its boiling point is 250 F., its azeotrope boiling point with water is 190 F., and the azeotrope ratio is 5.3 pounds of perchlorethylene to l pound of water. About B. t. u.s are required to evaporate 1 pound of perchlorethylene. Perchlorethylene is non-flammable and its toxicity characteristics render it reasonably safe to use, much more so than some of the chlorinated hydrocarbons not herev listed.

Among the presently known uorinated hydrocarbons having boiling point slow enough for convenient use in this invention are Vthe following, identified only by formulae and boiling points, as it is believed they are as yet without individual names.

Reference has been made heretofore to the use of plastics as additives v'for impregnation of the Wood. A number of the materials belonging to thisV broad class maybe used in connection with this invention. Among them' are those which Vmay advantageously be dissolved in an appropriate solvent and introduced into the re-vV tort with the wood, as are other treating solvents heretofore described, after the wood has been dried down almost to a desired final moisture content. To be useful in this manner the plastic material should readily penetrate the wood when in solution at temperatures below the solvent boiling point. If the plastic be .a thermo-setting plastic its setting temperature should be substantially higher than the water-solvent azeotrope boiling point, and preferably higher than the boiling point of the solvent in which the plastic is held in solution. After impregnation of the wood in a manner `similar to the impregnation procedures heretofore described, the solvent containing the unabsorbed plastic may be drained from the retort and the residual solvent may then be evaporated from the wood as an azeotrope vapor along with residual moisture in the wood, after which the wood may be heated by any appropriate means to the setting temperature of the plastic absorbed therein. If the setting temperature of the absorbed plastic is low enough the setting might be accomplished by heating the wood by means of steam while still in the retort. However, other means of heating the wood with or without pressure may be resorted to, if desired.

Whatever plastic is employed it is preferred that it shall not form ternary azeotropes with the water and solvent.

I may also use a thermo-plastic material or other plastic which will remain in solution in the solvent during and after impregnation and allow it to harden in the wood after the solvent has been drained and stripped therefrom.

For example, polystyrene may be dissolved in perchlorethylene and used as the impregnating material, after the wood is dried preparatory to that step. When the wood is thus impregnated with polystyrene and the solvent has been stripped therefrom the polystyrene hardens but not to a brittle state and the Wood thus impregnated is moisture resistant and acquires tremendous toughness and ability to resist Wear and abrasion. This type of plastic is especially valuable as a carrier of color, which suggests many possibilities of enhancing the appearance of the wood along with durability.

It will be recognized that the present invention lends itself readily to the economical and advantageous impregnation of wood by various suitable plastics within the retort following the drying of the wood.

This application isa continuation-in-part of my application Serial No. 176,385,l filed `luly 28, 1950, which was formally abandoned subsequent to the ling of the instant application.

While I have shown and described preferred methods and apparatus for the practice of this invention, it should be understood that numerous *changes and variations in the foregoingarc contemplated and may be made without departingn from the 'principles `andscope of the invention as expressed inthe claims which follow.

Having 'shown and described my invention, I claim:

`l. A wood treatment process which comprises submerging the vwood in 'a liquid bath in 'a -containerrclosed to `the atmosphere, Vsaid bath'containing asthe essential drying agent' a'halogenated'hydrocarbon solvent which is immiscible with and heavier than water, a'"solvent for resins, no'n-flammable,V and has Va constant watersolvent azeotropeiboiling pointjthe bathb ng'at Ya temperature range between the solvent boil @point andthe boiling point of the azeotrope of thewsolvlentwiih water, and while maintaining theV bathwvvithin ,the-Said temperature range, continuously drawing off fro'mthe bath the evolved azeotropic vapor withV its water content effective for maintaining thebath'water-free,thereby removing Vfrom the wood the more loosely held Vvportionrof thel water Vcontent thereof, thereafter effecting condensation of vapors within the wood "and'thereby causing the bath solvent `to penetrate the wood, subsequently resuming vaporization of moisture from the wood to remove the more tightly bound portion of the water content therefrom while drawing otf the evolved vapor with its water content, separatingY the wood from the liquid, subjecting the thus treated wood to sub-atmospheric pressure while removing solvent therefrom, raising the temperature of said wood, and again subjecting the resulting wood to sub-atmospheric pressure Vto remove residual solvents therefrom.

Z. A wood treatment process which comprises submerging the wood in a liquid bath in a container closed to the atmosphere,.said bath containing as the essential drying agent a halogenated hydrocarbon solvent which is immiscible with and heavier than water, a solvent lfor resins, non-flammable, and has a constant water-solvent azeotrope boiling point, the bath being at a temperature range between the solvent boiling point and the boiling point of the azeotrope of the solvent with water, and While maintaining the bath within the said temperature range continuously drawing olf from the bath the evolved azeotropic vapor with its water content effective for maintaining the bath water-free, thereby removing from the wood a first portion of the water content thereof, thereafter effecting the condensation of the vapors within the wood and thereby causing the bath solvent to penetrate` the wood, subsequently resuming vaporization of moisture from vthe wood to remove a second portion of the water content therefrom while drawing off the evolved vapor with its water content, subjecting the thus treated wood to sub-atmospheric pressure while removing solvent therefrom, then submerging the Wood in a liquid bath composed of a similar solvent containing a wood preservative of a character not to form ternary azeotropes with water and the solvent, increasing the pressure to which the treated wood is being subjected to atmospheric pressure, heating the liquid bath containing the submerged wood while removing water therefrom, separating Vthe thus treated wood from the liquid bath, subjecting the thus treated food to sub-atmospheric pressure to remove some solvent therefrom, raising the temperature of the thus treated wood, and again subjecting the wood to subatmospheric pressure while removing additional residual solvent therefrom.

3. The process of claim 2 wherein the food preservative is pentachlorophenol.

4. A wood treatment process which comprises submerging the wood in a container closed to the atmosphere in a liquid bath containing as the essential drying agent a halogenated hydrocarbon solvent which is immiscible with and heavier than water, a solvent for resin, nonammable, and has a constant water-solvent azeotrope boiling point, the bath being at a temperature range between 250 F. and 190 F. at atmospheric pressure and with thebath within said temperature range, continuously drawing off from the bath the evolved azeotropic vapor with its water content effective for maintaining the Abath water-free, said water removal being continued until the moisture content of the wood is not over about 50% by weight based on the wood, thereafter etfectingcondensation of vapors within the wood and thereby causing the bath solvent to penetrate the wood, subsequently resuming vaporization of moisture from Ythe wood to remove a desired amount of the more difcultly removable portion of the water content therefrom, while continuously draw# ing off the'evolved vapor with its water content,'separat ing the wood from vthe liquid, and subjecting the thus treated vwood to sub-atmospheric pressure while drawing off evolved vapors from the lower portion of the container.

References Cited in thele of this patent UNITED STATES PATENTS 247,602 Boulton sept. 27, 1881 (Other references on'followingepage) UNITED STATES PATENTS Nelson Oct. 12, 1909 Besemfelder Apr. 22, 1913 Edlich Nov. 5, 1935 Hollerer Nov. 22, 1938 Helson Oct. 8, 1940 Anderson et al. Mar. 14, 1950 Hudson Dec. 26, 1950 26 Smith ---.2 ..2 Apr. 10, 1951 Hertenstein June 23, 1953 OTHER REFERENCES 5 Special Methods of Seasoning Wood, Boiling in Oil, Report R1665, Forest Products Laboratory, Madison 5, Wisconsin, February 1947, 2 pages. 

2. A WOOD TREATMENT PROCESS WHICH COMPRISES SUBMERGING THE WOOD IN A LIQUID BATH IN A CONTAINER CLOSED TO THE ATMOSPHERE, SAID BATH CONTAINING AS THE ESSENTIAL DRYING AGENT A HALOGENATED HYDROCARBON SOLVENT WHICH IS IMMISCIBLE WITH AND HEAVIER THAN WATER, A SOLVENT FOR RESIN, NON-FLAMMABLE, AND HAS A CONSTANT WATER-SOLVENT AZEOTROPE BOILING POINT, THE BATH BEING AT A TEMPERATURE RANGE BETWEEN THE SOLVENT BOILING POINT AND THE BOILING POINT OF THE AZETROPE OF THE SOLVENT WITH WATER, AND WHILE MAINTAINING THE BATH WITHIN THE SAID TEMPERATURE RANGE CONTINUOUSLY DRAWING OFF FROM THE BATH THE EVOLVED AZETROPIC VAPOR WITH ITS WATER CONTENT EFFECTIVE FOR MAINTAINING THE BATH WATER-FREE THEREBY REMOVING FROM THE WOOD A FIRST PORTION OF THE WATER CONTENT THEREOF, THEREAFTER EFFECTING THE CONDENSATION OF THE VAPORS WITHIN THE WOOD AND THEREBY CAUSING THE BATH SOLVENT TO PENETRATE THE WOOD SUBSEQUENTLY RESUMING VAPORIZING OF MOISTURE FROM THE WOOD TO REMOVE A SECOND PORTION OF THE WATER CONTENT THEREFROM WHILE DRAWING OFF THE EVOLVED VAPOR WITH ITS WATER CONTENT, SUBJECTING THE THUS TREATED WOOD TO SUB-ATMOSPHERIC PRESSURE WHILE REMOVING SOLVENT THEREFROM, THEN SUBMERGING THE WOOD IN A LIQUID BATH COMPOSED OF A SIMILAR SOLVENT CONTAINING A WOOD PRE- 